In lots of U.S. cities, one of the most pressing infrastructure needs is a service everyone uses but no one likes to talk about: sewers. More than 40 years have passed since President Nixon signed the Clean Water Act into law. Many older sewer systems and wastewater plants built with federal money now need upgrades. And this time, local communities will have to pay the bill. NPR's Greg Allen reports in Miami, the county sewer system is so decrepit that some neighborhoods can't handle even one more toilet.

GREG ALLEN, BYLINE: Coconut Grove in Miami, even on a weekday, is a popular spot for shopping and dining along the tree-lined streets. But while some sidewalk cafes are bustling, Kent Knautz says his plans to open a Jimmy Johns sandwich shop here are on hold.

KENT KNAUTZ: So, yeah, we're actually paying rent right now, and we don't have a store.

ALLEN: Knautz is standing outside an empty storefront he's rented now for nearly a year. He says he was shocked when he took his plans to the county for approval.

KNAUTZ: They said that we could not add to the sewer structure. So we couldn't put a sink in, a mop sink, we couldn't add a bathroom. So we could build out our store, but they would not give us a certificate of occupancy.

ALLEN: Well over a dozen businesses are in a similar situation, unable to open or expand because of a moratorium on any new sewer hookups in Coconut Grove. It's because two pump stations which serve the area are over capacity, in violation of an agreement Miami-Dade County has with federal regulators.

Work is going on to upgrade the capacity at both pump stations. But to see it, you have to put on a hard hat and follow Miami-Dade Water and Sewer Department inspector Daniel Machado.

DANIEL MACHADO: It requires us going down some stairs.

ALLEN: OK. Great.

MACHADO: OK.

ALLEN: That would be fine.

MACHADO: All right.

ALLEN: A climb down a 20-foot ladder takes us to pump station 11. There are more than 100 other pump stations like this one also at capacity, putting a halt to new sewer hookups in other Miami neighborhoods. The crew here is installing new pumps, plus an emergency generator that will make sure the plant keeps operating during hurricanes and power outages. Important work, construction manager Robert Stebbins says, but something which gets little public attention.

ROBERT STEBBINS: Nothing glamorous about rehabbing sewer. It's all underground. You don't see anything when you're done, but you know you got a good product.

ALLEN: In Miami, like many cities, that out-of-sight, out-of-mind mentality led local officials to put off badly needed maintenance and improvements for years. That kept sewer and water rates low. But as a result, the county's dilapidated wastewater system is a long festering problem that's now become critical. Just watch the TV news.

(SOUNDBITE OF NEWS REPORTS)

UNIDENTIFIED MAN #1: What began as a small break has turned into quite a sinkhole that nearly swallowed a car.

UNIDENTIFIED MAN #2: Water is shooting into the air. It almost looks like Old Faithful.

ALLEN: Miami-Dade county engineers are called to respond to water and sewer line breaks almost daily. Some of them are catastrophic. After months of negotiations with the federal Environmental Protection Agency, the county recently agreed to spend $1.6 billion to make improvements to its sewer system and wastewater treatment plants. But to get it approved, Miami-Dade Mayor Carlos Gimenez had to go before the county commission with a sales pitch.

MAYOR CARLOS GIMENEZ: Now, we all know that water and sewer is not a sexy issue, but it is an absolutely fundamental - and it's absolutely fundamental to everything that we do.

ALLEN: That $1.6 billion is just the beginning. In all, Miami-Dade County is planning to spend more than $12 billion over the next 20 years to fix its water and sewer systems. And Miami's not alone. The EPA estimates that across the country, the cost of upgrading the nation's drinking water and wastewater systems in the next decade will top $125 billion.

One of the first and largest action items on Miami-Dade County's to-do list is here on a small island in the middle of Biscayne Bay.

ALEXIS SEGAL: This is the largest and oldest sewage treatment plant in Miami-Dade County.

ALLEN: Alexis Segal is with Biscayne Bay Waterkeeper, an environmental group that has long sparred with officials in Miami over sewage treatment and water quality issues. In its agreement with EPA, the county plans to spend more than a half-billion dollars to modernize its plant on Virginia Key. But Segal's group is asking the EPA to require more.

The sewage treatment plant here is less than 15 feet above sea level, vulnerable to storm surge and rising sea levels expected with climate change. Segal says the EPA should amend its agreement with the county to require it to do more to prepare for the consequences.

SEGAL: So making the existing walls thicker, building seawalls to go around it, perhaps raising up higher the existing buildings.

ALLEN: The deputy director of Miami-Dade's Water and Sewer Department, Doug Yoder, says that's exactly what the county is planning to do.

DOUG YODER: Yes, we're looking at fully coordinating our response with the reality that we are very vulnerable in southeast Florida to climate change and sea level rise.

ALLEN: Miami-Dade County's agreement with the EPA only covers violations of the Clean Water Act, a law written before climate change and sea level rise were envisioned. But Yoder says the EPA aside, as it spends billions upgrading its systems, the county plans also to storm-proof its wastewater plants and pump stations.

In the wake of Hurricane Sandy, there are measures also being considered in New York and other East Coast cities. That will make the cost of modernizing the nation's water and sewer systems even higher. Greg Allen, NPR News, Miami. Transcript provided by NPR, Copyright NPR.